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Macroscopic thermomagnetic convection: A more generic case and optimization

Cramer, A.; Zhang, X.; Gerbeth, G.

It was demonstrated in a previous paper that the interaction between a thermoelectric current j and an imposed static magnetic field B produced thermoelectromagnetic convection (TEMC). The prominent feature was utilisation of a wall material exhibiting a big difference in the thermoelectric power S in comparison to the fluid. Although high flow velocities were accomplished, the vigour was potentially mitigated by two design issues. Firstly, the side walls parallel to the temperature gradient Grad T were made from the same electrically high conducting material as the isothermal walls. This, in parts, shorts the thermoelectric current. Moreover, these walls might be seen as lowering the degree of the experiment of being generic. Secondly, the field created by a permanent magnet covered only a small fraction of the fluid volume. Again, albeit being mirror symmetric, the three-dimensional distribution of B lowers the degree of being generic.

The present paper reports on an experimental study on TEMC in a square box wherein the necessary Grad T is accomplished by heating and cooling of two opposing side walls, respectively, whereas the other two side walls are electrically non-conducting. An almost two-dimensional distribution of B is applied to a relatively large area of the interface between the fluid and the bottom of the container. The pole shoes of the magnet are specifically designed so as to have a high value of the curl of the Lorentz force, the non-vanishing of which is another pre-requisite for TEMC. Two containers with different bottom materials are build. The ferromagnetic nickel with negative S used in previous work is replaced by isotan in one variant, offering probably the highest absolute value of S among metals. To consider also the counterpart, nichrome with a high positive S is used in the construction of the second container. Ultrasonic Doppler velocimetry is employed to quantify the TEMC flow field. The results of all three configurations are compared and discussed. In addition, first results on more developed turbulent regimes are presented, which could not be reached in the previous setup because of a more limited Delta S x Delta T.

Keywords: Thermoelectricity; convection; liquid metal; electromagnetic stirring; static magnetic field

  • Magnetohydrodynamics 45(2009)4, 505-510

Permalink: https://www.hzdr.de/publications/Publ-13637
Publ.-Id: 13637